1. Field of the Invention
The present invention is related to a technology of an image forming apparatus, and more particularly to the technology for making load torque of a motor driving an intermediate transfer member or a transfer belt not be reduced when photoreceptors for colors are separated from the intermediate transfer member or the transfer belt.
2. Description of the Related Art
Recently, the number of electrophotographic devices, which includes a color printing function such as a color copier, a color printer, or a like, has increased.
Among others, the number of tandem type of the electrophotographic devices has increased in which a developing device is individually provided to each of a plurality of photoreceptors. Single toner images are formed on respective photoreceptors, and then sequentially transfer the single toner images to an intermediate transfer member (belt), and transfer a synthetic color image onto a sheet. In this case, in order to improve a life duration of the photoreceptors for colors, Japan Laid-open Patent No. 2006-139063 and a like disclose the photoreceptors other than photoreceptors for black and white are separated from the intermediate transfer member when a black and white image is formed. The intermediate transfer member is driven by a motor. The load torque for the motor driving the intermediate transfer member is different between a case of forming a color image and a case of forming the black and white image, depending on the number of the photoreceptors contacting with the intermediate transfer member.
Accordingly, in the black and white image formation, a torque for the motor is lower than a torque for the motor while conducting the color image formation, and there is a problem in that a stable motor control becomes difficult.